Both scientific and economic considerations make it desirable that the transgenic and control mice to be used in this program are house dat one central location. With respect to scientific considerations, the correlation of DNA repair deficiencies in different transgenic lines with spontaneous DNA damage, mutations and cellular senescence, necessitates the exclusion as much as possible of environmental variation. Hence, the need to wean and house the animals under uniform and well-controlled conditions. Economic considerations involved the cost-effectiveness of sharing organs/tissues,c ell lines and DNA samples. The Transgenic Animal Core will provide investigators of the three projects with all these biological materials upon request. It will import mutant and transgenic animals into the RIVM barrier facility, breed all transgenic lines into C57/BL/6, make the necessary crosses among the different lines, establish aging cohorts and determine survival of the individual transgenic lines, and perform complete histopathological examination of all organs and tissues.